Stihl 034 won't stay tuned

[wolfcreek]

Did a tuning on my old Stihl 034. ( the usual, warmed up / start one turn out on high and low / find mid point on low / adjust high for proper sound / adjust idle / tweak low and repeat the steps if needed ). Saw tuned great ( idle nice, no hesitation on throttle, drops back to a nice idle, cuts quick and runs cool ). Set the saw down for an hour and start it up no problem. Pick that same saw up the next day and fight to get it started. Runs way off not wanting to idle, chugging at full throttle. Go through the tuning from start again and get it running smooth. Settings on the carb always end up the same.

I'm picking up a carb kit to over haul the carb but wanted to bounce this off you guys because I'm wondering if it may be something more like crank seals on the way out? BTW - also replaced new fuel filter, line, air filter and pulse line before doing this tune up. I also have a few ms170's and a ms291, never had any issues starting them and keepin in tune.

[Al_Smith]

Sounds like seal .Most likely clutch side .

Typically on a seal on it's way out when tuned warm it will do okay at least for awhile .Once it cools down in has a tendency to run rich until it heats up again .

034 has some age to it which comes as no surprise it could use both a carb rebuild and a set of seals .Good saw though just needs a little attention .

[thecfarm]

wolfcreek,welcome to the forum.

[thenne1713]

Sounds to me to be temp sensitive, so I would more suspect carb mount or cylinder mount bolts being loose?  Seals I would expect to leak consistently. (IMHO:-)

Sounds like seal .Most likely clutch side .

Typically on a seal on it's way out when tuned warm it will do okay at least for awhile .Once it cools down in has a tendency to run rich until it heats up again .

034 has some age to it which comes as no surprise it could use both a carb rebuild and a set of seals .Good saw though just needs a little attention .

[Al_Smith]

What I've found on seals and again from  my experiance is they leak more so after a short run which causes them to heat up some. Of course if they are nearly gone they leak all the time .Completely blown  you'll find it nearly impossible to even start the saw .

[HolmenTree]

To alot of folks crankcase seals are one of the  most miss understood,  forgotten about or the last part to be changed on a saw.
Without the foundation of postive crankcase pressure  you can do all you want in repairs but you will never have a proper running saw .

[joe_indi]

Though all  symptoms point accusing fingers at the crank seals, I would also check the carburetor.If  LA (Idle adjust screw) is turned in more than necessary, similar problems could arise. Here is what I do for a 036: Turn in L and H fully, back them both out by 1 1/2 turns. Tun out the LA screw till the screw no longer touches the shaft. Check for full closing of the butterfly valve. If its not fully closed when held against the light a sliver of light would be visible on the seating area of the butterfly. If this happens loosen the holding screw of the shutter and re-align it. Once this  is done turn in the LA screw till a sliver of light is visible at one side of the butterfly. Try starting now. If everything else is fine the saw will run rich at idle and stall without your hand at the throttle. Turn in the LA till the saw barely idles. Let it warm up, then turn in L and back off LA to get a smooth idle. Go  to full throttle, turn in H till 4 stroking stops and the saw screams. Back off H till screaming stops and 4 stroking starts. If the problem persists after all this, yes check the seals, and, also the cylinder gasket.

Joe

[nell6355]

just had the same thing happen.  Check the easy stuff like fuel line leaks, bad carb seals. crap in the fuel filter.  But if the tune is CHANGING as you run the saw for an hour, there is a good chance you are leaking air into the crankcase.   If your idle leans out, and the chain won't stop at idle, it's just like mine.  Sorry for the bad news but the clutch bearing wore out my crankcase bearing bore by about 0.010 so it's a rebuild and new case for me.  My saw shop says they could patch the case but it wouldn't last.   If you pull the clutch and remove the oiler, push fore and aft on the crankshaft with your thumb.  If the bearing moves at all in the bore, you're sucking air.    Get it pressure tested.